Steam turbine part including ceramic matrix composite (cmc)

ABSTRACT

A steam turbine part includes a ceramic matrix composite (CMC). The part may be made wholly or partially of CMC. The CMC eliminates the possibility of oxidation and thus increases steam turbine availability and reliability

BACKGROUND OF THE INVENTION

The invention relates generally to steam turbines. More particularly,the invention relates to a steam turbine part including ceramic matrixcomposite (CMC).

In steam turbines, valves open and close openings between sections ofthe turbine and are exposed to steam under pressure. One of the designcriteria for any steam turbine is reliability, followed by availabilityand operability. Valve stems, which are typically made of a Nickelalloy, are subjected full steam pressure and temperatures. Thesepressure and temperatures can reach up to 24.8 mega Pascals (MPa) (3600pounds per square inch (psi)) and 621° C. (1150° F.) in current designs.Next generation steam turbines, however, are expected to reach up to29.6 MPa (4300 psi) and 760° C. (1400° F.). Under these latterconditions, Nickel alloy valve stems will oxidize and build up oxide.The valve stem is expected to have up-down motion in a bushing made ofsimilar material. Thus, both valve stem and bushing may develop oxide.To maintain reliability, it is necessary to sustain sufficient clearanceat the design and manufacturing stage, so as to allow the stem to worksmoothly until major overhaul and/or replacement of the stem (typically5-10 years) can be performed. One approach to solve this solution isproviding additional clearance for the oxide. Unfortunately, providingexcessive clearance results in steam leakage which impairs performance.In addition, at high steam temperatures, any reasonable engineeringclearance (e.g. 10 millimeter radial) will disappear due to oxidebuild-up on Nickel based super-alloys in probably 2-4 years, thuspotentially resulting in valve stem binding, making the valvenon-functional. If a stem binds in its normal, valve open condition,such an event may result in an inability to shut off steam flow andover-speeding of the turbine.

BRIEF DESCRIPTION OF THE INVENTION

A steam turbine part includes a ceramic matrix composite (CMC). The partmay be made wholly or partially of CMC. The CMC eliminates thepossibility of oxidation under which a layer of partially or fully oxidebased ceramic/fiber combination is applied, and thus increases steamturbine availability and reliability.

A first aspect of the disclosure provides a steam turbine part for asteam turbine, the stationary part comprising: a ceramic matrixcomposite.

A second aspect of the disclosure provides a steam turbine comprising: apart including a ceramic matrix composite.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective partial cut-away illustration of a steamturbine.

FIG. 2 is a cross-sectional view of a steam turbine part in the form ofa valve stem made completely of ceramic matrix composite (CMC).

FIG. 3 is a cross-sectional view of a steam turbine part in the form ofa valve stem made partially of CMC.

FIG. 4 is a cross-sectional view of a steam turbine part in the form ofa valve stem having only surfaces exposed to steam made of a CMC.

FIG. 5 is a cross-sectional view of a steam turbine part in the form ofa valve stem made of a CMC having a textured exterior surface.

DETAILED DESCRIPTION OF THE INVENTION

At least one embodiment of the present invention is described below inreference to its application in connection with and operation of a steamturbine. However, it should be apparent to those skilled in the art andguided by the teachings herein that the present invention is likewiseapplicable to any suitable turbine and/or engine. Embodiments of thepresent invention provide a steam turbine part where the stationary partincludes a ceramic matrix composite (CMC).

Referring to the drawings, FIG. 1 shows a perspective partial cut-awayillustration of a steam turbine 10. Steam turbine 10 includes a rotor 12that includes a rotating shaft 14 and a plurality of axially spacedrotor wheels 18. A plurality of rotating blades 20 are mechanicallycoupled to each rotor wheel 18. More specifically, blades 20 arearranged in rows that extend circumferentially around each rotor wheel18. A plurality of stationary vanes 22 extends circumferentially aroundshaft 14, and the vanes are axially positioned between adjacent rows ofblades 20. Stationary vanes 22 cooperate with blades 20 to form a stageand to define a portion of a steam flow path through turbine 10.

In operation, steam 24 enters an inlet 26 of turbine 10 and is channeledthrough stationary vanes 22. Vanes 22 direct steam 24 downstream againstblades 20. Steam 24 passes through the remaining stages imparting aforce on blades 20 causing shaft 14 to rotate. At least one end ofturbine 10 may extend axially away from rotor 12 and may be attached toa load or machinery (not shown) such as, but not limited to, agenerator, and/or another turbine.

In one embodiment of the present invention as shown in FIG. 1, turbine10 comprises five stages. The five stages are referred to as L0, L1, L2,L3 and L4. Stage L4 is the first stage and is the smallest (in a radialdirection) of the five stages. Stage L3 is the second stage and is thenext stage in an axial direction. Stage L2 is the third stage and isshown in the middle of the five stages. Stage L1 is the fourth andnext-to-last stage. Stage L0 is the last stage and is the largest (in aradial direction). It is to be understood that five stages are shown asone example only, and each turbine may have more or less than fivestages. Also, as will be described herein, the teachings of theinvention do not require a multiple stage turbine.

As understood, steam turbine 10 includes a number of parts. For purposesof description, the invention may be described relative to a stationaryvalve stem 102, as shown in FIGS. 2-4. Other stationary parts mayinclude, for example, a stationary valve bushing 104 (FIGS. 2-3), anozzle, casings, etc. It is also understood that the teachings of theinvention may also be applied to moving parts such as a valve head orrotor blade. Part 100 includes a ceramic matrix composite (CMC). CMC mayinclude any ceramic material, perhaps including reinforcing fiber orfabric weave, capable of resisting oxidation. In one embodiment, CMCincludes an oxide based matrix, which acts to eliminate oxidation. Forexample, CMC 110 may include an aluminum oxide (Al₂O₃) matrix. In analternative embodiment, CMC 110 may also include silicon carbon (SiC)fibers to increase hardness. In another embodiment, CMC 110 includes anoxide based matrix and a ceramic based fiber. For example, the oxidebased matrix may include (Al₂O₃), titanium boride (TiB) and siliconcarbon (SiC). In another example, the oxide based matrix may includeAl₂O₃, titanium di-boride (TiB₂), platinum carbon (PtC) or siliconcarbon (SiC). The ceramic based fiber may include any of theabove-listed oxide-based matrices or a ceramic based material such assilicon carbon (SiC). Other matrices may include, for example, zirconiumcarbide (ZrC), hafnium carbon (HfC), titanium carbon (TiC), tantalumcarbon (TaC), and niobium carbon (NbC) and mixed carbides such aszirconium silicon carbon (Zr—Si—C), hafnium silicon carbon (Hf—Si—C) ortitanium silicon carbon (Ti—Si—C). Other fibers may include, forexample, silicon carbon (SiC), carbon (C), alpha-Al₂O₃ with yttriumoxide (Y₂O₃) and zirconium oxide (ZrO₂) additives, or variationsthereof. In any event, CMC 110 should act to increase the ductility orenergy absorption in the material system for part 100 and the capabilityto resist steam corrosion and wearing which in certain cases may includelayers on the CMC 110 or fibers.

In one embodiment, shown in FIG. 2, part 100 may be made entirely ofCMC. In an alternative embodiment, shown in FIG. 3, part 100 may be madepartially of CMC. In the example shown, part 100 includes a CMC layer112 over a metal core 114, e.g., of steel. In this case, a thermalmatching interface 116 may be necessary between CMC layer 112 and metalcore 114 to aid in matching the different thermal expansion rates.Thermal matching interface 116 may include, for example, a compliantlayer between CMC layer 112 and metal core 114. Alternatively, as shownin FIG. 4, only surfaces 118 of a part 100 that are exposed to steam mayinclude CMC 110. As understood, a variety of configurations may beemployed within the scope of the invention.

Part 100 may be formed using any now known or later developed technique,e.g., creating a pre-preg of reinforcing material as a freestanding partor mounted to a metal core 114 (FIG. 3), repeatedly infusing the prepregwith a ceramic and curing the ceramic.

Referring to FIG. 5, in one alternative embodiment, an exterior surface120 of part 100 may include a textured surface 120. Textured surface 120may be formed, for example, by providing a woven textile fabric as anouter portion of a pre-preg such that the fabric creates the texturedsurface 120. The increased surface area for the steam path created bytextured surface 120 may increase efficiency by reducing leakage.

Although embodiments of the invention have been described relative to avalve stem for a steam turbine, the teachings should not be so limited.In particular, the invention can be applied to practically any part of asteam turbine for which oxidation is a limiting factor. For example, theteachings of the invention may be applied to nozzles, casings, etc.

The above-described invention increases steam turbine availability fornext generation steam turbines through reduction of oxide growth rates.

The terms “first,” “second,” and the like, herein do not denote anyorder, quantity, or importance, but rather are used to distinguish oneelement from another, and the terms “a” and “an” herein do not denote alimitation of quantity, but rather denote the presence of at least oneof the referenced item. The modifier “about” used in connection with aquantity is inclusive of the stated value and has the meaning dictatedby the context, (e.g., includes the degree of error associated withmeasurement of the particular quantity). The suffix “(s)” as used hereinis intended to include both the singular and the plural of the term thatit modifies, thereby including one or more of that term (e.g., themetal(s) includes one or more metals). Ranges disclosed herein areinclusive and independently combinable (e.g., ranges of “up to about 25wt %, or, more specifically, about 5 wt % to about 20 wt %”, isinclusive of the endpoints and all intermediate values of the ranges of“about 5 wt % to about 25 wt %,” etc).

While various embodiments are described herein, it will be appreciatedfrom the specification that various combinations of elements, variationsor improvements therein may be made by those skilled in the art, and arewithin the scope of the invention. In addition, many modifications maybe made to adapt a particular situation or material to the teachings ofthe invention without departing from essential scope thereof. Therefore,it is intended that the invention not be limited to the particularembodiment disclosed as the best mode contemplated for carrying out thisinvention, but that the invention will include all embodiments fallingwithin the scope of the appended claims.

1. A steam turbine part comprising: a ceramic matrix composite.
 2. Thesteam turbine part of claim 1, wherein the CMC is a layer over a metalcore.
 3. The steam turbine part of claim 2, further comprising a thermalmatching interface between the CMC and the metal core.
 4. The steamturbine part of claim 1, wherein the CMC includes an oxide based CMC. 5.The steam turbine part of claim 4, wherein the oxide based CMC includesaluminum oxide (Al₂O₃).
 6. The steam turbine part of claim 5, whereinthe CMC further includes silicon carbon (SiC).
 7. The steam turbinestationary part of claim 1, wherein the CMC includes an oxide basedmatrix and a ceramic based fiber.
 8. The steam turbine stationary partof claim 7, wherein the oxide based matrix includes aluminum oxide(Al₂O₃), titanium boride (TiB) and silicon carbon (SiC).
 9. The steamturbine part of claim 7, wherein the oxide based matrix includesaluminum oxide (Al₂O₃), titanium di-boride (TiB₂), platinum carbon (PtC)and silicon carbon (SiC).
 10. The steam turbine part of claim 1, whereinthe CMC includes: a matrix selected from the group consisting of:zirconium carbide (ZrC), hafnium carbon (HfC), titanium carbon (TiC),tantalum carbon (TaC), niobium carbon (NbC), zirconium silicon carbon(Zr—Si—C), hafnium silicon carbon (Hf—Si—C) and titanium silicon carbon(Ti—Si—C); and a fiber selected from the group consisting of: siliconcarbon (SiC), carbon (C) and alpha-Al₂O₃ with yttrium oxide (Y₂O₃) andzirconium oxide (ZrO₂).
 11. The steam turbine part of claim 1, whereinan exterior surface of the part includes a textured surface.
 12. Thesteam turbine part of claim 1, wherein the part includes a stationarypart.
 13. The steam turbine part of claim 12, wherein the stationarypart is selected from a group consisting of: a valve stem, a nozzle, anda bushing.
 14. A steam turbine comprising: a part including a ceramicmatrix composite.
 15. The steam turbine of claim 14, wherein the CMC isa layer over a metal core.
 16. The steam turbine of claim 15, furthercomprising a thermal matching interface between the CMC and the metalcore.
 17. The steam turbine of claim 14, wherein the CMC includes anoxide based CMC.
 18. The steam turbine of claim 17, wherein the oxidebased CMC includes aluminum oxide (Al₂O₃).
 19. The steam turbine ofclaim 18, wherein the CMC further includes silicon carbon (SiC).
 20. Thesteam turbine of claim 14, wherein the CMC includes: a matrix selectedfrom the group consisting of: zirconium carbide (ZrC), hafnium carbon(HfC), titanium carbon (TiC), tantalum carbon (TaC), niobium carbon(NbC), zirconium silicon carbon (Zr—Si—C), hafnium silicon carbon(Hf—Si—C) and titanium silicon carbon (Ti—Si—C); and a fiber selectedfrom the group consisting of: silicon carbon (SiC), carbon (C) andalpha-Al₂O₃ with yttrium oxide (Y₂O₃) and zirconium oxide (ZrO₂).